Related Clues:

• It may smear
• Tattoo fluid
• Hard-to-erase stuff
• Common breast-pocket stain
• Indelible liquid
• Fountain pen filler
• Write stuff?
• HP product
• It's held in a squid's 37-Down
• Printer's medium
• Liquid from a squid
• Fluid from cuttlefish
• Liquid for writing
• Liquid used to write
• They always go on ahead, blow them!